The present invention relates generally to systems which fabricate semiconductor wafers, and more specifically to a device which provides a rapid transfer of semiconductor wafers into and out of the vacuum chamber of an electron beam lithography system.
The development of the direct-write e-beam lithography system poses a number of challenging requirements in the area of substrate handling. Silicon substrates must be routinely and rapidly transferred between a vacuum chamber and an environment characterized by room temperature and normal atmospheric pressure.
Perhaps the most significant challenge is posed by the throughput requirements for semiconductor wafer production. For example, a rate of ten to fifteen substrates per hour represents an order of magnitude of throughput increase over existing e-beam fabrication systems. For practical purposes, this rate precludes the conventional use of hand-loaded cassettes, indicating total automation of the load function is required. The substrate loader must be a carrier-to-carrier system, requiring no human contact with substrates.
The task of providing a rapid transfer of semiconductor substrates into a lithography system to generate sub-micron device geometries is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated by reference:
U.S. Pat. No. 3,954,191 issued to Wittkower et al;
U.S. Pat. No. 3,968,885 issued to Hassan et al;
U.S. Pat. No. 4,009,785 issued to Trayes;
U.S. Pat. No. 4,047,624 issued to Dorenbos;
U.S. Pat. No. 4,293,249 issued to Whelan; and
U.S. Pat. No. 4,425,075 issued to Quinn.
Hassan et al disclose a method and apparatus for handling semiconductor wafers which are moved into and out of a vacuum chamber. Pattern writing by an electron beam produces precise patterns on the wafer chips. Rapid transfer of workpieces is achieved with an elevator that functions as a transfer mechanism from an antechamber to a vacuum chamber.
Wittkower et al teach an isolation lock through which wafers can move in a path between first and second regions at different pressures. The patented vacuum lock comprises a housing having an upper wafer entrance and a lower wafer exit at opposite sides of the housing, and a piston in the housing with a wafer receiving surface. A pressure lock for handling workpieces is also shown in the Dorenbos patent.
Whelan discloses a semiconductor handling system operated by a computer and including a track of air or gas for moving the semiconductor slices along. An air track for semiconductor wafers is also shown in the Trayes patent. In Quinn the wafers are aligned by means of air jets.
While the systems in the above-cited references are instructive, the need remains to provide a system for the rapid transfer of a production line of semiconductor wafers into and out of the vacuum chamber of an electron beam lithography system. The present invention is intended to satisfy that need.